Phosphorylation and dephosphorylation are ubiquitous processes within cells that greatly influence cellular phenotypes. The extent and duration of phosphorylation is regulated by the opposing action of phosphatases, which remove the phosphate moieties. Consequently, considerable attention has been devoted to the characterization of tyrosine kinases and tyrosine phosphatases and their associations with disease states (Zhang, Crit. Rev. Biochem. Mol. Biol., 1998, 33, 1-52).
Protein tyrosine phosphatases are signaling molecules that regulate a variety of cellular processes, including cell growth and differentiation, cell cycle progression and growth factor signaling. A number of protein tyrosine phosphatases have been implicated as negative regulators of insulin signaling (Zhang, Crit. Rev. Biochem. Mol. Biol., 1998, 33, 1-52). Characterization of the protein tyrosine phosphatase PTPRU revealed it to be a member of the type II receptor protein tyrosine phosphatase (rPTP) subfamily, which includes PTP.mu. and PTP.kappa. PTPRU contains many of the domains characteristic of this subfamily, including a transmembrane domain and two tandem intracellular protein tyrosine phophatase domains. In addition, the presence of the extracellular immunoglobulin (Ig) domain and four tandem fibronectin-type III (FN-III) repeats, which are common to cell-adhesion receptors, suggests that PTPRU can contribute to the mechanisms of cell adhesion and homotypic cell interactions (Avraham et al., Gene, 1997, 204, 5-16; Crossland et al., Biochem. J., 1996, 319 (Pt 1), 249-254; Thomas et al., J. Biol. Chem., 1994, 269, 19953-19962; Wang et al., Biochem. Biophys. Res. Commun., 1997, 231, 77-81; Wang et al., Oncogene, 1996, 12, 2555-2562). PRPRU also contains a MAM domain, which, along with the Ig-like domain, is required for the homophilic interactions displayed by PTP.mu. and PTP.kappa. (Avraham et al., Gene, 1997, 204, 5-16; Crossland et al., Biochem. J., 1996, 319 (Pt 1), 249-254; Wang et al., Biochern. Biophys. Res. Commun., 1997, 231, 77-81; Wang et al., Oncogene, 1996, 12, 2555-2562).
Owing to its simultaneous identification in several different cell types, PTPRU is known by many synonyms, including protein tyrosine phosphatase, receptor type, U, also known as PTP-RU or PTPU2; protein tyrosine phosphatase receptor omicron or PTPRO; protein tyrosine phosphatase pi; protein tyrosine phosphatase J or PTP-J; pancreatic carcinoma phosphatase 2, PCP2 or PCP-2; protein tyrosine phosphatase psi, receptor type, R-PTP-Psi, PTPPsi or pi R-PTP-Psi; glomerular epithelial protein 1 or GLEPP1; and FMI.
The expression of PTPRU is developmentally regulated. During early development expression is mainly in the brain and lung. In adults, PTPRU expression is in the kidney, lung, heart, skeletal muscle, pancreas, liver, prostate, testis, brain, bone marrow, and stem cells (Avraham et al., Gene, 1997, 204, 5-16; Crossland et al., Biochem. J., 1996, 319 (Pt 1), 249-254; Wharram et al., J. Clin. Invest., 2000, 106, 1281-1290; Beltran et al., J. Comp. Neurol., 2003, 456, 384-395; Stepanek et al., J. Cell Biol., 2001, 154, 867-878). PTPRU is additionally involved with megakaryopoiesis, cell adhesion and promotion of the G0/G1 cell cycle arrest in normal naïve quiescent B cells (Taniguchi et al., Blood, 1999, 94, 539-549; Aguiar et al., Blood, 1999, 94, 2403-2413; Yan et al., Biochemistry, 2002, 41, 15854-15860).
A number of tissue-specific forms of PTPRU have been identified. In the kidney, PTPRU is known as GLEPP1 and is highly expressed in podocytes, specialized epithelial cells that form the glomerular capillaries (Thomas et al., J. Biol. Chem., 1994, 269, 19953-19962). In megakaryocytes, PTPRU is called PTPRO, alternative splicing of which yields a lymphoid tissue-specific, truncated form called PTPROt (Aguiar et al., Blood, 1999, 94, 2403-2413). Alternative splicing of PTPRU also yields osteoclastic protein tyrosine phosphatase or PTP-oc (Amoui et al., J. Biol. Chem., 2003, 278, 44273-44280).
In addition to participation in the regulation of several essential functions, PTPRU is implicated in numerous disease conditions. Motiwala et al., have reported a correlation between PTPRU and diet dependent development of pre-neoplastic nodules and hepatocellular carcinoma (Motiwala et al., Oncogene, 2003, 22, 6319-6331). PTPRU expression was found to be altered in several cancerous cell lines (Crossland et al., Biochem. J., 1996, 319 (Pt 1), 249-254; McArdle et al., J. Invest. Dermatol., 2001, 117, 1255-1260; Wang et al., Biochem. Biophys. Res. Commun., 1997, 231, 77-81; Wang et al., Biochem. Biophys. Acta., 1999, 1450, 331-340). Furthermore, PTPRU was found to be hypermethylated in colon cancer (Mori et al., Cancer Res., 2004, 64, 2434-2438).
The diverse tissue distribution and disease associations of PTPRU indicate that it can be an appropriate target for therapeutic intervention in a number of disease conditions.
Currently, there are no known therapeutic agents that effectively inhibit the synthesis and/or function of PTPRU. Consequently, there remains a long felt need for agents capable of effectively inhibiting PTPRU synthesis and/or function.
Generally, the principle behind antisense technology is that an antisense compound hybridizes to a target nucleic acid and effects the modulation of gene expression activity, or function, such as transcription or translation. The modulation of gene expression can be achieved by, for example, target RNA degradation or occupancy-based inhibition. An example of modulation of target RNA function by degradation is RNase H-based degradation of the target RNA upon hybridization with a DNA-like antisense compound. Another example of modulation of gene expression by target degradation is RNA interference (RNAi) using small interfering RNAs (siRNAs). RNAi is a form of antisense-mediated gene silencing involving the introduction of double stranded (ds)RNA-like oligonucleotides leading to the sequence-specific reduction of targeted endogenous mRNA levels. This sequence-specificity makes antisense compounds extremely attractive as tools for target validation and gene functionalization, as well as therapeutics to selectively modulate the expression of genes involved in diseases.